Young Adult and Middle Grade are fast becoming the dominant genres for new fiction. I heard at a writers’ conference recently that one publishing house has fired most of its adult fiction editorial staff and replaced them with YA/MG editors. Many of our most creative authors are now penning books aimed primarily at young people.

I’ve also noticed that most newly minted agents rep primarily YA/MG, and even many established agencies are switching focus to teen/tween fiction.

I suspect this can be explained in three words: “Harry Potter/Twilight.” Kid Lit is where the money is. Publishers are willing to take chances with the genres because the rewards can be so high. (Harry is MG; Twilight is YA.)

Nobody talks about this, but I also think the relatively lower advances for children’s books create a more flexible marketplace. Plus there has traditionally been more open communication between children’s editors and new writers. (My YA writer friends routinely get reads from editors without an agent as go-between.)

So a lot of us who have been writing for adults are now taking a look at these genres and want to know what the YA rules are—and what distinguishes it from MG.

Basically, it’s the age of the target reader—currently about 13-21 for YA and 8-13 for MG.) Word count isn’t so important any more, since many MG books are huge (witness J. K. Rowling’s tomes.)

If you aren’t in the habit of reading YA, go check out the shelves of your local bookstore or library. This fiction is as sophisticated as a lot of stuff for adults, and its themes can be even more “adult” than what's allowed in a lot of mainstream romance and mystery lines. It can also be more literary. In fact, some literary novels originally written for adults have found their ultimate success as YA. (Catherine Ryan Hyde’s Pay it Forward is an example.)

Another important factor to keep in mind is something I learned at a recent writers’ conference: the YA audience is mostly female.

Marketers believe boys stop reading books when they reach puberty. (I have some argument with that, but it’s what statistics say, I guess.) I think this is why Harry Potter is called MG rather than YA—not so much because of the actual age of the characters—since they age through the series—but because it’s popular with both genders.

If you're writing action, adventure, and epic fantasy aimed at boys as well as girls, it’s best to start with a young main character and call it MG. But if you’re dealing with sophisticated emotions and relationships, it can be YA—and pretty much anything goes. As long as your protagonist is under twenty.

So could it be that in the near future, teenaged girls will dictate the literary marketplace instead of a bunch of persnickety old dudes?

Maybe so. When I think of my own teenaged reading habits, I’m not sure that would be an entirely good thing, but it might bring some fun new changes.

And for those of us trying to scale the walls of the seemingly impenetrable fortress that is American publishing, change has to be good.